<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        ul{
            margin: 0;
            padding: 0;
            list-style: none;
        }
        ul{
            width: 805px;
            margin: 0 auto;
            /* border: 1px solid #000; */
        }
        ul li{
            border: 1px solid red;
            width: 200px;
            height: 200px;
            float: left;
            margin-right: -1px;
        }
        .clearfix::after{
            content: "";
            display: block;
            clear: both;
        }
    </style>
</head>
<body>
    <ul class="clearfix">
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
    </ul>
</body>
</html>